The one who designed that can't possibly have seen a Wii U.
He just took a couple of images from Google Images, put them together, and slapped a Pikmin 3 logo on the gamepad.
Otherwise how could that have happened?
Nonetheless it's a pretty funny screwup, and I'm betting most people who have not seen a Wii U will not even realize the mistake.

That's what Nintendo gets for focusing too much on the controller during marketing. Remember E3 2012? They barely even shown the console. No one cares about the controller unless the system it's controlling is decent.

They should have also dropped the Wii branding. "Wii" has a bad connotation in gaming community. Wasn't the code name "Nintendo Stream"? They should have just called it that.